This invention relates to a liquid chromatograph with a fraction collector and more particularly to such a liquid chromatograph using a mass analyzer as the fraction collector.
As a technology related to liquid chromatography, it has been known to provide a fraction collector on the downstream side of the flow route so as to selectively collect only a target component contained in a sample. Normally, the part of a liquid chromatograph serving to collect a fraction (herein referred to as the "fraction collecting device") includes a liquid pump, a sample injector, a column, a detector, a fraction collector and a system controller for controlling the collection of the fraction. When the detector detects the peak of the target component, the device functions so as to activate a switch valve when the component corresponding to this peak arrives at the switch valve of the fraction collector for its collection. An ultraviolet visible light detector is usually used as the detector for monitoring the sample solution flowing through a flow cell provided on the downstream side of the column.
Recently, a mass analyzer is coming to be used instead of an ultraviolet visible light detector for collecting a fraction with high accuracy. A prior art fraction collecting device for a liquid chromatograph using a mass analyzer as its detector is shown in FIG. 1 wherein numeral 1 indicates a liquid pump, numeral 2 indicates a sample injector, numeral 3 indicates a column for separating components, numeral 4 indicates a splitter, numeral 5 indicates a system controller, numeral 6 indicates a mass analyzer serving as a detector, numeral 7 indicates a fraction collector, numeral 8 indicates a flow route for carrying out the analysis, numeral 9 indicates a fraction collector flow route, and numeral 10 indicates a control unit comprising a personal computer. A fraction collecting device using a mass analyzer as its detector is characterized as being provided with a splitter 4 for branching the flow route into the route for analysis 8 connected to the mass analyzer and the fraction collector flow route 9 connected to the fraction collector. The flow rate of the mobile phase is normally maintained at about several tens of ml/min when the collection of a fraction is carried out, but since the maximum flow rate to the mass analyzer is only 2 ml/min, only a small portion of the sample solution eluted from the column 3 is arranged to be branched into the mass analyzer 6. Since the mass analyzer 6 analyzes a sample solution by ionizing it and its collection becomes difficult after the analysis, only a portion of the sample solution is used for the analysis and the rest is directed for collection.
Thus, a fraction collecting device for a liquid chromatograph is provided with a splitter on the downstream side of the column but the conditions for the collection of fraction such as the flow rate of the mobile phase must be varied, depending on the kind of the sample to be fractioned. In addition, the mode of ionization such as the electro-spray method and the atmospheric chemical ionization method must also be modified. Thus, the split ratio by means of the splitter must also be adjusted such that an optimum condition can be obtained.
It has been known to exchange the fraction collector flow route from the splitter to the fraction collector in order to change the split ratio until a desired split ratio is obtained according to the sample. It is cumbersome, however, to actually exchange the flow route. The manners in which the screws are tightened may even cause deformations of the pipes and a change in the dead volume.